1. Technical Field of the Invention
The present invention relates to a sheath type measuring instrument for use in directly measuring a physical property of a measurand, which is covered with an outer wall such as a casing or the like and is disposed in an inner wall, such as the temperature of a thrust pad of a thrust bearing disposed in a casing, for example, a bearing incorporating such a sheath type measuring instrument for monitoring at all times the temperature of a member exposed to a high temperature, such as a thrust pad or the like, and a rotary machine having a rotatable shaft (main shaft) rotatably supported by such a bearing.
2. Description of the Related Art
Rotary machines such as pump apparatus or the like, for example, have a rotatable shaft (main shaft), which rotates at a high speed, rotatably supported by bearings. The bearings include a radial bearing for bearing radial loads and a thrust bearing for bearing a thrust load. The thrust bearing generally has a thrust pad or the like which is held in sliding contact with a rotor and hence generates heat. It has been desirous to monitor at all times the temperature of a member exposed to a high temperature, such as a thrust pad or the like, and to hold the temperature at or below a predetermined temperature.
It has been practiced to directly measure the temperature of above-described thrust pad or the like with a sheath type measuring instrument which has a thermocouple or a thermoresistor housed in a sheath (metallic protective tube) and an insulation such as of magnesia or the like filled between the thermocouple or the thermoresistor and the sheath, the sheath being of a reduced outside diameter. When the sheath type measuring instrument is used to measure the temperature of members such as thrust pads or the like which are relatively narrow and are closely disposed, there is less danger of disconnection than if a thermocouple or a thermoresistor is directly wired to thrust pads or the like.
Heretofore, as shown in FIG. 7, a sheath type measuring instrument 10 has a thin linear sheath (metallic protective tube) 12 housing a thermocouple or a thermoresistor in its distal end and filled with an insulation, and a barrel 14 for fixing the sheath 12 while positioning in position. The sheath 12 has a proximal portion telescopically held in the barrel 14 by a spring or the like. For directly measuring the temperature of a measurand 22 having a heat generating region 20, disposed in an outer wall 16 such as an outer casing or the like and covered with an inner wall 18 such as an inner casing or the like, using the sheath type measuring instrument 10, a barrel mount hole 24 for mounting the barrel is bored in the outer wall 16 and a sheath insertion hole 26 for inserting the tip end of the sheath 12 therein is bored in the inner wall 18 and the measurand 22 in alignment with the barrel mount hole 24. With the tip end of the sheath 12 being located in position in the sheath insertion hole 26, an externally threaded tapered surface 14a on the lower outer circumference of the barrel 14 of the sheath type measuring instrument 10 is threaded into the barrel mount hole 24 in the outer wall 16, thereby fastening the barrel 14 to the outer wall 16 to hold the sheath 12 in position.
According to another scheme, as shown in FIG. 8, a clearance hole 27 having a larger inside diameter than the diameter of the sheath 12 is bored in the outer wall 16, and the barrel 14 of the sheath type measuring instrument 10 is mounted on the outer wall 16 with a flange 28 that is large enough to close the clearance hole 27. The flange 28 attached to the outer wall 16 is positionally adjusted to absorb a positional deviation δ1 between the center O1 of the clearance hole 27 and the center O2 of the sheath insertion hole 26 by bringing the axis of the barrel 14 and the sheath 12 into alignment with the center O2 of the sheath insertion hole 26.
For measuring the temperature of a measurand with the sheath type measuring instrument, if the sheath insertion hole for inserting the tip end of the sheath therein is of an inside diameter that is much greater than the diameter of the sheath, for example, then the temperature cannot accurately be measured because of a heat gradient within the sheath insertion hole. Therefore, the inside diameter of the sheath insertion hole is required to be of substantially the same as the diameter of the sheath.
If the sheath insertion hole is a hole (narrow hole) having substantially the same inside diameter as the diameter of the sheath, then as shown in FIG. 7 referred to above, for example, when the sheath 12 is to be located in position to install the sheath type measuring instrument 10 after boring the barrel mount hole 24 in the outer wall 16 and boring the sheath insertion hole 26 in the inner wall 18 and the measurand 26, the barrel mount hole 24 and the sheath insertion hole 26 need to be highly positionally accurate with respect to each other. Therefore, it may be necessary to take into account a case where the barrel mount hole 24 and the sheath insertion hole 26 are to be machined after the parts are assembled. Specifically, as shown in FIG. 9, in the event that a positional deviation δ2 occurs between the center O3 of the barrel mount hole 24 and the center O4 of the sheath insertion hole 26, even if the positional deviation δ2 is slight, since the axis of the barrel 14 and the sheath 12 is aligned with the center O3 of the barrel mount hole 24, the sheath 12 interferes with the open end of the sheath insertion hole 26. Therefore, the sheath 12 cannot smoothly be inserted into the sheath insertion hole 26. If the sheath 12 is forcibly inserted, it may be deformed or damaged.
If, as shown in FIG. 8, the positional deviation δ1 between the clearance hole 27 bored in the outer wall 16 and the sheath insertion hole 26 bored in the inner wall 18 and the measurand 22 is to be absorbed by the flange 28, then a complex process is required to move the flange 28 to a position where the tip end of the sheath 12 can be inserted into the sheath insertion hole 26 and to position and fix the flange 28, for example.